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ISSN : 1226-9654
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Vol.18 No.4
Abstract
In this study, we investigated the effect of spatial frequency filtering on facial expression recognition and age perception. Two experiments were performed to compare the relative importance of high spatial frequency information with low spatial frequency information on facial information processing. In the first experiment, the stimuli were made from eight images of facial expressions which were located on the 2-dimensional space of emotion: pleasure-displeasure and arousal-relaxation. In the second experiment, the images used stimuli were the female faces from twenties to sixties. The spatial frequency filtering of facial stimuli were similar to Vuilleumier, Armony, Driver, & Dolan(2003)'s. The results showed that the high spatial frequency information are more decisive than low spatial frequency information in the estimation of the facial expressions on both pleasure and arousal dimensions, and both high and low frequency information are concerned with the estimation of age for the old groups. These results imply that the age perception is related to both pathways of changeable information processing and invariant information processing on the face.
Abstract
It has been well known that there are two kinds of texture segregation mechanisms; first-order texture detecting mechanism of linear processing, and second-order mechanism of nonlinear processing. The importance of spatial frequency selectivity has been demonstrated in constructing higher level of pattern perception from local texture segregated area. This study using a probability distribution space consisted of independent mean and variance dimensions measured segregation thresholds of various directions of texture pairs in space. Five spatial frequencies were applied to each direction respectively. In this space, two mechanisms were confirmed as previous studies identified; one was luminance-sensing, the other was negatively rectifying, luminance-and-contrast-sensing. Their thresholds varied similarly across the spatial frequencies, were peak at the same spatial frequencies, 1.16 cycles/degree. When an identical stimulus pattern was prepared to measure first- and second-order texture properties, similar selectivity of spatial frequency between two mechanisms was observed. It was discussed that two stage model could be used for the observed similarity of spatial frequencies between two texture detection mechanisms and general notion of second-order filter's tuning to lower spatial frequency than first-order.
Abstract
Despite its therapeutic success in treating major depression, little is known about the mechanism by which repetitive transcranial magnetic stimulation (rTMS) alters physiological responses of neurons. To elucidate cellular processes underlying rTMS, we compared the effect of rTMS on hippocampal long-term potentiation (LTP) with those of electroconvulsive shock (ECS) and fluoxetine. Male Wistar rats were subjected to chronic mild stress (CMS) regimen, an animal model of depression, for six weeks. Anhedonia, a behavioral symptom of depression, was tested by measuring sucrose consumptions. There was a significant difference in sucrose intake between nave and CMS-exposed animals. The rats were then treated with one of the three conditions: rTMS (rTMS), sham rTMS (SHAM), ECS (ECS), or fluoxetine (FLX) for two weeks. Following two weeks of treatments with rTMS, sham rTMS, ECS, or fluoxetine, they were anesthetized and LTP was induced in vivo in the perforant path-dentate gyrus synapses. Field excitatory postsynaptic potentials (fEPSP) were monitored for 50 min after the LTP induction. LTP induction was impaired in CMS (sham rTMS) and FLX group compared to the nave control group. The potentiated fEPSP of the ECS group was marginally different from that of NAVE group, showing a trend toward impaired LTP. On the other hand, LTP was recovered to the level of nave animals in rats treated with rTMS. These results suggest that rTMS has a rescuing effect on electrophysiological properties of the hippocampal neurons by reversing the impaired synaptic efficacy caused by the CMS procedure and that the antidepressant effect of rTMS might be mediated by its protective action on the synaptic plasticity.